This research addresses the roles of experience, particularly learning and physical exercise, in developing and maintaining a healthy brain. The "acrobat" motor learning vs. exercise paradigm tests thehypothesis that routine physical exercise-associated neural activity can alter the brain capillary network and possibly modulate neurogenesis with little direct effect upon the synaptic network, whereas motor learning, can alter synapses and may affect neuronal survival, with minimal effects upon vasculature. In this paradigm, learning with relatively minimal exercise occurs in the "Acrobat"condition (AC),which requires rats to traverse a challenging elevated obstacle course. Exercisewith minimal learning is accomplished in rats given voluntary exercise (VX) in an activity wheel or forced exercise (FX) on a treadmill. For baseline purposes, an inactive condition (1C)involves rats kept individually in standard cages, and other control and exercise conditions are occasionally also used, such as a motor control (MC)group that merely walks in response to prodding to control for handling. We have found changes in cerebellar and cerebral cortical synapses in the AC group but not in the other 3 groups. In contrast, increased vascularization, relative to 1C,occurs in the VXand FXgroups, but not in the AC group. In parallel recent work, we have also demonstrated neuron addition in the adult rat motor cortex and are investigating effects ofthese manipulations upon it. We are also examining electrophysiological correlates of the morphological plasticity of synapses in motor cortex. We propose to use morphological and morphometric, electrophysiological, and behavioral methods in mature adult rats to 1)determine electrophysiological correlates of learning-induced morphological changes in adult rat cerebral cortex, 2) further characterize morphological plasticity of neurons and non-neuronal tissue in adult rat cortex, 3) assess the extent to which neuron addition occurs in the adult rat motor cortex and its modulation by the exercise and motor learning manipulations, and 4)assess vascular plasticity in response to physical exercise in adult rat brain. As results clarify which of these variables are most sensitive to experience and potentially valuable targets for aging self-intervention, this work will be extended to the aging brain.